Such an apparatus of this general type is disclosed in German Auslegeschrift No. 1 454 765. One end of the cutter housing, through which the granules are discharged by means of water which is simultaneously used for conveying and cooling purposes, is mounted on a flange provided on an extrusion device. The other end of the cutter housing rests on the shaft for the cutter device. A V-belt drive pulley means for effecting fine-adjustment, in an axial direction, of the spacing between the cutter device and the nozzle plate, and a pneumatic piston and cylinder arrangement for effecting axial displacement of the cutting unit are all mounted on the blade shaft.
It is extremely important, in such an apparatus, to be able to set the spacing between the rotating cutter device and the nozzle plate very accurately. However, it is equally important that this, setting, once determined, is maintained during the operation of the granulator.
Extruded strands of material, such as polyethylene, emerge from the nozzle plate at an elevated temperature which may be as high as 250.degree. C. The rotating cutter device cuts the extruded strands into granules which are cooled and conducted away for discharge by water fed into the cutter housing.
The nozzle plate needs to be at a high temperature to prevent the plastics material from hardening in the small diameter bores of the nozzle. If such hardening occurs, the material will, of course, block the bores.
However, the temperature of the nozzle plate also causes the cutter housing to be heated. An obvious consequence of such heating is uncontrolled thermal expansion of the housing. This expansion may cause displacement of the mounting connected to the housing for the blade shaft. This means that the pre-set spacing between the rotating cutter device and the nozzle plate changes. A reduction in the spacing produces considerable wear on the rotating cutter device and on the surface of the nozzle plate. On the other hand, if the spacing increases, poor granulation results because granules tend, in such a case, to drag filaments with them and cause congestion of the nozzle plate.